The general form of the game is that you play several different
characters.  Different puzzles are presented and solved as
different characters.  When the game begins, you are
Blackthorne, but later you can (must?) be Mariko, Toranaga,
etc. in various situations.

Some puzzles are pretty clearly defined.  These are marked
with a *.  For others, it's not obvious what the puzzle is. 
These are marked with a ?.

Puzzles:

* As Blackthorne, you must navigate the Erasmus through the
storm and reef into Anjiro harbor.  This is primarily just a
puzzle where you must steer the Erasmus in the right
direction.  Minor additional parts include being lashed to
the rudder, commanding the sails to be reefed, etc.

? As Blackthorne, you must learn Japanese.  How this is done
is an open question.

* As Blackthorne, you must rescue Rodrigues when he is washed
overboard.  This may include convincing Hiro-matsu to let
you go ashore, finding Rodrigues (?), causing Yabu to climb
down the cliff (since the guards won't let you do it),
attracting his attention to the ledge, etc.

* As Blackthorne, you must help Toranaga escape from Osaka. 
This would be in several parts.  First, you must notice that
Toranaga and Kiritsubo switch places.  Second, you must
distract Ishido and the guards.

* As Toranaga, you must get to the galley through the maze of
Osaka's streets.  I see this as a maze-type puzzle where
there are bands of Ishido's Grays and an ambush at some
point by "bandits."  At some point in the maze is the place
where you find your extra men (the sign of a fish).  At some
time after the ambush, Ishido will know you've escaped, and
more Grays will arrive.

? As Toranaga, you must negotiate with Ferriera and the
Jesuits to get out of the harbor.  How this is done I
haven't a clue.

* As Blackthorne, you must maneuver the galley out of the
harbor by staying close to the frigate, but not too close.

* As Blackthorne, you must teach Toranaga to dive.  This might
be too hard; instead there could be a swimming race puzzle,
where you must try to beat Toranaga.

* As Blackthorne, you must threaten (and mean!) to commit
seppuku, but the timing must be perfect, otherwise you will
succeed.  You must bring things to a head just as Omi is
ready to stop you.

? As Mariko, you must teach Blackthorne Japanese.  How?

? As Mariko, you must try to commit suicide.  How to make this
more than just a timing puzzle?  It is important to not do
it before Ishido gives in.  Maybe you should play someone
other than Mariko in this puzzle?  Ishido?

* As Blackthorne, you must fight the ninja during the attack,
help Mariko escape into the secret room, not open the door
when the ninja say they only want you, break the bolts on
the other door, not stop Mariko, etc.

? As Toranaga, you must detect Yabu's treachery?


Overall Puzzles:

As Toranaga, you are constantly trying to influence people
to come over to your side.  How to do this?  Possibilities
include a diplomacy-type structure, a swapping structure
("Offer Izu to Yabu," "Tell Zataki about Ochiba," etc.). You
must also delay things as much as possible after your escape
from Osaka.  Perhaps various people come to you with
information, as Gyoko does in the book.  To get the
information, you have to consent to speak with them.  Some
of it is true, some is not, and you must act on the true
information.  This might also be how Omi reports the news
about Yabu's betrayal during the attack.  There are various
"players" you can negotiate with.  These include the other
regents, the Jesuits, Ferriera, some of your own people
(such as Yabu), Blackthorne, Mariko, etc.  They will ask for
things, and you have to decide what to give them.  You also
have limited resources to give away, and if you promise them
twice, you might get in trouble (like Ishido giving the
Kwanto to both Zataki and Kiyama).

Learning Japanese.  This is a puzzle for both Blackthorne
and Mariko.  Perhaps there is a vocabulary you must learn,
and as Blackthorne, you can only communicate through an
interpreter or in Japanese.  As the game progresses, you
have less access to an interpreter.  One implementation
problem is that some Japanese words are longer than 9
characters, for example "wakarimas-u" vs. "wakarimas-en".

Scoring.  Your score as each character must depend on how
you are doing at achieving your goals.  As Toranaga, it's
your influence.  As Blackthorne, it could be your
proficiency in Japanese, and your adoption of Japanese
customs.  Suppose that at various points, Blackthorne is
given options.  One is a "barbarian" option, and one is a
"japanese" option.  Examples would include eating meat vs.
not eating meat, or wearing European clothes vs. wearing a
kimono.  These might be scored subtly (not appear on the
status line, for example?)